If everything is predictable in a game, that isn't much fun. RNGs, or Random Number Generators, are a way to introduce a touch of randomness and causality you need to spice it up.
In this article, we'll learn how random number generators work.
How an Analogic Random Number Generator Works
The simplest form of a RNG is throwing dice or flipping coins.
Using a single die or coin means that each value has the same probability of occurring. Using multiple dice or coins instead will give a lower probability to the highest and lower values, and a higher probability to the middle values.
The oldest known tabletop game, the Royal Game of Ur, uses four 4-sided dice. Each die can give a value of 0 or 1 meaning that the value obtained by a single dice throw can go from 0 to 4.
There are 16 possible combinations, of which one gives a value of 0, 4 gives a value of 1, 6 gives a value of 2, 4 gives a value of 3, and one gives a value of 4.
In this case there is a 1/16 or 6.25% chance of getting 0, 1/4 or 25% chance of getting 1, 3/8 or 37.5% chance of getting 2, 1/4 or 25% chance of getting 3 and 1/16 or 6.25% change of getting 4.
More complex games have manuals full of tables to determine something randomly.
Any game that uses dice has an analogic random number generator.
How Random Number Generators Work in Video Games
In video games, RNGs are much less noticeable and more complex, and players might not even be aware they exist. There are many ways you can generate a Random Number, but how do you actually use one?
Breaking it down into the simplest terms, using a RNG is not dissimilar from what you saw above with the dice throw used to determine an effect from a table. You just don't see the dice throw.
In a video game, you can use a RNG to determine what kind of loot might be dropped by a fallen enemy, or what you can find in a chest, or what kind of random encounter will await you, or even what the weather will be.
RNGs are used, for example, to live up open world games without the developers having to code every single section of forests and roads and deserts. Instead, developers code some possibilities and let chance determine what happens when the player reaches a certain point in the map.
Will you meet a bear, a wolf pack, or some bandits? The game does its version of rolling a die to determine that.
Let's see how to code a simple example of a Random Number Generator to better understand how they actually work.
How to Code a Random Number Generator
Most programming languages contain a
random function. This function returns a random number, and what kind of random number depends on its implementation.
Math.random() returns a random number between 0 (included) and 1 (not included). In Python,
randint from the
Let's consider a pretty common video game situation: we have an enemy that often drops a common item, but now and then drops something rare. This enemy may be, for example, a wolf that could drop a wolf pelt (common) or a wolf fang (rare).
How do you determine what is "rare"? That depends on you – it can be that 1 in 10 drops is a rare item, or that 1 in 100 drops is a rare item. A middle ground may be a chance of 1 in 25 for a rare items. And to complicate it a bit, there could be also a 1 in 10 chance of no item.
In this case you would need a function that returns a value between 0 and 1.
A chance of 1 in 25 is 4%, and a chance of 1 in 10 is 10%. In decimal form that would be 0.04 and 0.1, respectively.
In this case you can say that a number in the range from 0 to 0.04 gives the rare item, and a number in the range from 0.9 to 1 gives no item.
To avoid sticking to one language, let's first see how we can code this using pseudocode. This is not a real programming language – rather, it's a way to break down the code logic. It's like taking notes, as it's personal and will have varied syntax depending on the person writing it.
FUNCTION wolfDrop randomNumber = random(0,1) IF randomNumber < 0.04 THEN -> wolf fang ELSE IF randomNumber < 0.9 THEN -> wolf pelt ELSE -> empty END IF END FUNCTION
Or a more verbose version:
Create a function called
wolfDropand inside it store a random number between 0 (included) and 1 (excluded) in the
randomNumberhas a value less than
0.04the drop will be a wolf fang, else if the
randomNumberhas a value less than
0.9the drop will be a wolf pelt, and otherwise there will be no drop.
With the pseudocode ready, we can implement the code snippet in any language. Let's see, for example, how to code it in a few different languages:
(Thanks to alpox for the code snippets in Clojure, Golang, Kotlin, Elixir and C#, and to Jeremy for the snippets in Rust, C, and Julia.)
Other examples of math.random
Random Number Generators, or RNGs, are used in many games. In this article, you have learned how and why they are used, and you've seen an example implementation.
Next time you play a video game, will you be able to spot where a RNG may be used?